Fan-favorite Doctor Who companion Sarah Jane Smith was almost very different. In 1973, Doctor Who introduced the Third Doctor's new companion, Sarah Jane Smith. Played by Elisabeth Sladen, Sarah Jane was a journalist who stumbled upon a Sontaran plot and soon wound up working alongside the Doctor. There's a sense in which Sarah Jane's debut marked a turning point in the show's history; Jon Pertwee's tenure as the Doctor had largely been Earthbound, with the members of an organization called UNIT serving as series regulars, and Sarah's introduction moved a step away from UNIT at last.
Sarah Jane is generally seen as the greatest companion of classic Doctor Who. No damsel in distress, she was curious and resourceful, and she was there for many of the best Doctor Who stories - including the unforgettable "Genesis of the Daleks." Russell T. Davies actually brought Sarah Jane Smith back after he relaunched Doctor Who in 2005, and it wasn't long before she was starring in her own spinoff TV series, The Sarah Jane Adventures. This ran for five seasons, until Elisabeth Sladen sadly passed away in 2011.
But Sarah Jane Smith could have been very different - because she wasn't actually the first actress cast for the role (h/t Bad Wolf Archives). Producer Barry Letts originally cast an actress called April Walker for the role of Sarah Jane Smith, a tall blonde performer who had worked alongside Doctor Who star Jon Pertwee before. Speaking to Fantom in 2020, Walker recalled what she called an "adventurous audition." It was conducted as though it was a read-through, incorporating acting terrified, climbing away over walls and fences, falling in a faint, and even emotion; it was the longest audition she'd ever done, lasting an hour and a half. Letts was convinced April Walker was the right person for the role, but unfortunately he'd neglected to consult Third Doctor Jon Pertwee on the decision.
Pertwee felt Sarah Jane should be a short, probably dark-haired girl who could be thought of as his daughter. In contrast, he believed Walker would feel like his mistress, and that wouldn't be right for a children's program. And so Letts had little choice but to look for another actress, eventually settling on Elisabeth Sladen. It was undoubtedly the right decision, although it wasn't at all fair on April Walker, who had signed contracts and even been measured for her costume. Appropriately enough, the signing of that contract meant she did actually get paid for the season. The full story was kept secret until long after Pertwee, Letts, and Elisabeth Sladen herself had all passed away.
It's fascinating to imagine how different Doctor Who would have been had April Walker played Sarah Jane Smith. Pertwee's fears were probably exaggerated, but the reality is that the dynamic would certainly have been very different; the fatherly affection between the Third Doctor and Sarah Jane was a big part of what made her popular, and Tom Baker built upon this when he worked alongside her as the Fourth Doctor. It's hard not to conclude Pertwee made the right call, even if it did mean Doctor Who treated a talented actress very badly indeed.